1. Field of the Invention
The present invention relates to a guide wire, particularly to a guide wire used to guide a catheter in a body lumen such as a blood vessel.
2. Description of the Related Art
Guide wires are used to guide a catheter in treatment of sites at which open surgeries are difficult or which require minimally invasiveness to the body, for example, PTCA (Percutaneous Transluminal Coronary Angioplasty), or in examination such as cardio-angiography. A guide wire used in the PTCA procedure is inserted, with the distal end projecting from the distal end of a balloon catheter, into the vicinity of a target angiostenosis portion together with the balloon catheter, and is operated to guide the distal end portion of the balloon catheter to the target angiostenosis portion.
A guide wire used to insert a catheter into a blood vessel complicatedly bent requires appropriate flexibility and restoring performance against bending, pushability and torque transmission performance (generically called “operationality”) for transmitting an operational force from the proximal end portion to the distal side, and kink resistance (often called “resistance against sharp bending”). To obtain appropriate flexibility as one of the above-described performances, there has been known a guide wire configured such that a metal coil having flexibility is provided around a small-sized core member at the distal end of the guide wire, or a guide wire including a core member made from a superelastic material such as an Ni—Ti alloy for improving the flexibility and restoring performance.
Conventional guide wires include a core member that is substantially made from a single material. In particular, to enhance the operationality of the guide wire, a material having a relatively high elastic modulus is used as the material of the core member. The guide wire including such a core member, however, has an inconvenience that the distal end portion of the guide wire becomes lower in flexibility. On the other hand, if a material having a relatively low elastic modulus is used as the material of the core member for increasing the flexibility of the distal end portion of the guide wire, the operationality of the proximal end portion of the guide wire is degraded. In this way, it has been regarded as difficult to satisfy both requirements associated with the flexibility and operationality by using a core member made from a single material.
A guide wire intended to solve such a problem has been disclosed, for example, in U.S. Pat. No. 5,171,383, wherein a Ni—Ti alloy wire is used as a core member, and the distal side and the proximal side of the alloy wire are heat-treated under different conditions in order to enhance the flexibility of the distal end portion of the alloy wire while enhancing the rigidity of the proximal side of the alloy wire. Such a guide wire, however, has a problem that the control of the flexibility of the distal end portion by heat-treatment has a limitation. For example, even if it is successful to obtain a sufficient flexibility of the distal end portion of the alloy wire, it may often fail to obtain a sufficient rigidity on the proximal side of the alloy wire.